Tony is perceived differently by different people in the novel. Danny sees Tony, at first, as a flesh and blood person. Until the end of the novel, Tony's face is obscured by shadow and distance. Danny isn't sure who he is. Jack and Wendy think Tony is your standard imaginary friend, one who happens to coincide with Danny's frightening episodes of wild utterings and trances. Dr. Edmonds, Danny's psychiatrist in Sidewinder, thinks Tony is a product of Danny's mind, brought forth by family stress. Readers don't quite know what to make of him, though he seems a fairly benevolent figure in spite of his radical communication techniques.
When Tony finally reveals himself to Danny before Danny's showdown with Jack, we are told:
And now Tony stood directly in front of him, and looking at Tony was like looking into a magic mirror and seeing himself in ten years […], as if Tony – as if the Daniel Anthony Torrance that would someday be – was a halfling caught between father and son a ghost of both […]. (54.34)
Ah ha! The is the first time we've heard that Danny's middle name is Anthony (same as Jack's father), which alludes to the doubling and foiling of the complex father-son conflicts in The Shining, as we discuss in Jack's analysis. Also, if Tony is Danny at fifteen, then Tony's presence has all along foretold Danny's survival. Tony knows what could happen at the Overlook if Danny makes a wrong move, because some of the things have already happened, and Tony was already there.
He lived, but until the Overlook is destroyed the crazy script will keep repeating, like the 1945 masquerade ball, holding Tony in the middle, in limbo. Speaking of 1945, this passage also contains Jack's age, thirty, which means he was born in 1945, same year evil takes over the Overlook for good. That's what's meant by the word halfling. Tony is half Jack's age and is sort of a midpoint between Jack and Danny.
Since Tony has lived to see fifteen, he's had time to reflect. Though, he does have a good grasp on the situation, he isn't an especially great communicator. Maybe if he tried explaining things calmly to Danny instead of scaring the heck out of him, or showing him signs he can't read, Danny would have a better chance. But that wouldn't be very scary, now would it?